OK, I think you've misused the
%..._scheme_obsolete
according to:
https://fedoraproject.org/wiki/Packaging/ScriptletSnippets#GConf
%gconf_schema_obsolete is used for schemas that this package previously provided but no longer does.
So,
%pre
%mateconf_schema_prepare .../desktop_mate_peripherals_keyboard_xkb.schemas
%mateconf_schema_obsolete .../desktop_mate_peripherals_keyboard_xkb.schemas
is definitely not right here.
I think the %mateconf_schema_obsolete call should simply be dropped (for now, until when/if we want to investigate if the 3rd-party mate repo has any schemas in need of obsoletion)
While we're at it,
%mateconf_schema_prepare %{_sysconfdir}/mateconf/schemas/desktop_mate_peripherals_keyboard_xkb.schemas
should just be:
%mateconf_schema_prepare desktop_mate_peripherals_keyboard_xkb
(ie, each scriptlet should use the basename of the schema, not the full path)

The .desktop file modification is required for some fedora releases, f18+ is ok afaik. The rest of the mate stack is using X-Mate currently, thought it best to switch these over all at once instead of piece-meal.
I'll check on the dir ownership and licensing situation now, thanks

In fact, that's just desktop-file-validate that do not like using Mate category, the code is likely using the same category all over the place.
If mate was pushed only on f18 as planned ( after all, that's the whole point of doing a fedora 18 feature ), it would not be a issue.
And I think that using X-MATE will break some applets, I am looking at source code to check, but there is surely a issue there. So far, i only found it being used in the bundle copy of egglib in mate-panel, and not elsewhere. I guess upstream will likely know what is the specific version to us.
But I doubt it does work with both, and I doubt upstream used a substring match ( since that would be prone so error, and slower ).

I would treat that as a serious bug, and I would have blocked the review if I was the reviewer, yes. But since the review was approved, I am just raising the issue so this can be fixed in time.
Since mate desktop is not planned to be complete in F18 ( ie, there is lots of others packages part of mate, see https://github.com/mate-desktop/, and Dan answered that for example, the screensaver is not part of the feature to have it in F18 ), I am not sure people will really report if a applet is missing until the day of the release, or will just think "this is a work in progress, that's normal if something is not here".
Another fix would be to backport desktop-file-utils so everything will be correct, and make sure the correct value is used right from the start. If we keep a mess, we are just increasing the technical debt, and the source code of mate is already full of stuff that should be cleaned ( like for example migration code that do not work since the word "gnome" have been changed for "mate" in constant, so nothing will be migrated at all , so the code is useless )

Thanks Michael for your concerns. They will be taken in to consideration. If you have anything else to add in terms of actually fixing things instead of trying to block MATE please let is know.
Thanks,
Dan.

Dan, his concerns are valid, even if we disagree on their severity or blocker-worthiness. I know it can be frustrating, but invalidating those concerns with comments like "instead of trying to block MATE" is inappropriate. It's ok to *repectfully* disagree.